RFID systems are well known and the prior art is replete with different types of RFID systems, different applications for RFID systems, and different data communication protocols for RFID systems. Briefly, an RFID system includes two primary components: a reader (also known as an interrogator); and a tag (also known as a transponder). The tag is a miniature device that is capable of responding, via an air channel, to a radio-frequency (RF) signal (an interrogation signal) generated by the reader. The tag is configured to generate a reflected RF signal in response (a response signal) to the RF signal emitted from the reader. The reflected RF signal is modulated in a manner that conveys identification data back to the reader.
Because RFID tags respond via radio-frequency transmissions, a single reader or interrogator is often incapable of determining the position of the source of the RFID response signals. For example, a reader can receive a response signal from a tag without learning how far from the reader the tag is, or in which direction from the reader the response signal emanates. Accordingly, it can be difficult to measure position and distance properties of RFID tags with a single RFID reader.